daleburr

There are some threads already about this subject, but most are either from 2005, or just have a few "no one races that anymore" responses. So I thought I'd create a discussion to provide my experience of racing this!

I've become pretty annoyed with rubber tyres:

• They give good performance for a very limited time. On asphalt its really just one run. Carpet a meeting or two if you want a decent grippy tyre.
• They're inconsistent between sets. Some brands are better than others, but I've used multiple brands where sets handle different.
• They're awful on hot asphalt. You can run a harder tyre to withstand the heat, but then you just have less grip.

So, having run foams on my old F103 and Pro10 I decided it was time for a change! Some nitro foams were ordered.

Wheel options:

• Contact 26mm (front) tyres all round, for ease of fitment. It turns out the fronts are made of a much harder foam, so that gave zero traction.
• Contact 26mm/30mm. This handled much better, good traction now. But the Contact rims don't fit electric cars well; the spokes are huge and jam the suspension.
• Matrix 26mm/30mm. These rims are much better. With the kit hexes on my T4 I can run the wheels/tyres without modification. Just have to sand the rear lower shock balljoint to prevent rubbing the wheel.

For compounds I've tried:

• 35 rear and 37 front. Good traction, but the rear tyres wore 4 times faster than the fronts. Nightmare constantly truing the front tyres down to keep all 4 even.
• 37 all round. Wear a bit more even, but rears still wearing faster than the front.
• 37 rear and 35 front like the nitro guys use. Initially a step back for handling (less traction), but with some setup changes it's now even better and the wear is more even.

Diameters:

• The car is full-time 4wd, but there's enough slip on the foams to cope with small diameter differences.
• It likes a slightly larger diameter rear tyre (or both the same). If the fronts are larger diameter than the rear the handling is terrible.
• I true the rears to 64mm, the fronts to 63mm. The rears still wear a little faster than the fronts so over time they even up. True them again after 5 runs to get the stagger back.
• They probably get faster the more you run them (up to a point). So run new ones for practice, then they'll get quicker over the race event and be mega come the finals.

Wear:

• Indoors I did 5 meetings (25 races) on one set of tyres. And they were ~1s a lap faster than rubbers. Rubbers would last 3 meetings on this carpet, and be slow by week 3.
• Outdoors maybe 10-12 runs from a set of Matrix tyres. Rubbers would do maybe 8-10 runs in mod, and would be miles off the pace by run 10.
• This is running modified or 13.5 boosted on tracks that are pretty abrasive (ETS carpet indoors, course asphalt outdoors).

Setup:

• Alu flex chassis. I tried the carbon chassis outdoors as that's what I'd normally run on rubber. The Alu was loads faster (0.5s) as the carbon was edgy and carried no corner speed.
• Thicker shock oil than rubbers (500 instead of 450). I need to going thicker still as 450->500 was a big improvement.
• Thicker diff (7k instead of 4k). I need to going thicker still as 5k->7k was a big improvement.
• Kit wheel hexes (helps with wheel clearance, and stability).
• Droop is 3.5mm rear and 3mm front, measured over ride-height.
• Spider Blue additive indoors. Might not be necessary; the tyres get pretty sticky.
• Spider Red tyre additive outdoors. This stuff is amazing, it's very aggressive so works even on a hard nitro tyre.
• Cheap velcro (wrap-around) tyre warmers outdoors. UK tracks aren't generally very warm and we don't do warm-up laps, so these are helpful in the early laps against rubber drivers.
• I check the ride-height and droop each run. You could probably do every other run. Once I'm more comfortable with the tyres I'll alternate a few sets and save some work.

Conclusions:

• Foams are way more fun to drive. There's more grip, and they're much less edgy than rubber tyres. Win win.
• I make less mistakes on foams even though I'm going a lot faster. When I get it wrong, it just slides a bit more. Very progressive.
• They're crap if it's very cold (<15deg track temp) or if there's any moisture on the track.

For club racing I won't be going back to rubber tyres except to do a bit of national practice. I'll probably do crap at the nationals as I'll wonder where all the grip has gone. Oh well!

daleburr

Rear setup.


Front setup.


Clear Gorilla tape to protect the chassis. This stuff is amazing!
And vernier visible; you'll always have one on the table running foams.

fathead

I run at least 3 sets of foams for a day (well did, we quit running foams outdoors years ago, but still run them indoors on astro, but I'm just getting back into it and trying out some new foams), all pre-trued to the same size, then run in each set in practice, then 1 set for each race (we generally run 3 races), that way you don't get the small problem of them getting smaller (or wearing different) over a day and mucking with the setup.
Nitro foams, 26mm fronts on front and 26/30mm rears on rear, generally 35sh all round, if running 26mm all round I would run 2 pairs of rears to 1 pair of fronts to even wear, and yes generally 0.5-1mm bigger dia rears, if running 30mm rears then I would be next shore up, so 37sh instead of 35sh, then wear is pretty even with fronts.
We don't use sauce at all (foam or rubber)

You should be able to get UFRA foams easily enough in UK I would think to try as well

/edit These are ZAC Project foams, used to be Kawahara

Scott_T

iTrader: (5)

We race a foam tyre 10.5 blinky class on opposite weekends to our rubber tyre classes. The cars are really nice to drive. I'm using pretty much a rubber setup, but with 3 degrees camber front and rear. Using Ulti 26mm fronts, 30mm rears, 35sh front, 38sh rear. No tyre additives.

I normally true the tyres to the same diameter, but I might try leaving the rears a touch larger next time. I bring a few sets with me so ride height and droop changes are minimal (or not done at all!).

Scott_T

iTrader: (5)

And the wheels look so much better that the plain discs that rubber tyres generally use! These are Xceeds.

daleburr

I forgot to mention the looks, the black spoked wheels look cool as f**k, especially with the shell you've done there. That looks like a proper DTM car (as well as having DTM grip level if it's anything like mine).

Sean B.

iTrader: (13)

daleburr

TypeS shell works really well for foam and rubber. Seems to have the most downforce and stability of the TC shells

daleburr

What compounds? Carpet or asphalt? And how are you getting on against the rubber cars?

Sean B.

iTrader: (13)

daleburr

Do you find much performance difference between a 35sh 26mm (cut-down rear) tyre and a 37sh 30mm tyre?

I started on 35sh 26mm cut-down rears but the wear was huge. So I switched to 30mm 37sh; I found slightly less traction if anything, but wear massively reduced. Only thing is it can be hard for some cars (e.g. Mi6) to fit a 30mm rim.

DesertRat

iTrader: (2)

A few tips:

1: Front diff. Running a spool and foamies can cause a slide-and-grab feel in the front end that can cause excessive front end push at speed followed by too much low speed steering and inconsistent feel. A front diff will have more steering but with tuning can carry more speed, and you can play with the diff oil of course.
2: The standard front spring when running foam on my old Losi Type R was 30 pounds per inch. You read that right. The rubber tire setup was about 17 pounds per inch. You have to keep that nose off the ground.
3: You won't need nearly as much rear toe-in, probably.
4: Suspension setups generally had a much more aggressive camber gain, with a lot more angle in the links than rubber tire cars.
5: Swaybars were generally not as common, springs were relied on to carry the car weight.
6: As little as 0 droop was common. Some pre-load could even be used against the droop screw, if you can believe it.
7: BUT because of this heavily restricted suspension setup it was pivotal to keep the chassis as straight as a laser beam, I don't much like bubble-level tweak boards so I use scales, straight edge, and piece of tile to keep everything straight and weight even. The best way I found to make sure the chassis was straight was to take all of the tires off and set it flat on my piece of tile to see if it sits flat, then test the chassis spring coefficient in both directions by gently twisting the chassis to see how much force it takes to twist the edges of the chassis off the tile. If you can't tell the difference, its probably pretty close. Once the chassis is flat you can set ride height confidently, and have even weight on all four tires.

fathead

I found the balance to be pretty similar, maybe a touch more steering but nothing that needed a setup change, have to pay a bit more attention to camber with the wider foams though I think.

Evening up the wear was the point of it though and it works well there, but yes some cars have difficulty fitting the 30mm on the rear

Conrad

iTrader: (3)

Raced foam TC for years until it slowly died a death. 19t brushed back in the day on foams was easily one of my favourite classes to race Racers got fed up with constantly adjusting gearing and ride height/droop to accommodate for tire wear and moved to rubbers.

My findings are very similar to DesertRat:
Foams should be run only with diff's, spools can cause alot of damage when you hit something with this much grip.
I used to run 40 or 42 fronts with 37 rears with no additive on primafelt GT. This was with 26mm wide foams (ATS).
You really need three pairs of rears, true them 1-2mm larger than the fronts and alternate between the rear pairs every run.
Springs were 26lb front, 20lb rear with a 1.7mm front ARB, no rear ARB.
Droop was about 1.5-0.5mm normally. 1.5-2.0' rear toe in.
You do need to keep an eye on your rollout as a few mm in tire wear makes a big difference to your rollout.
I never built a RC Crew Chief model for my old foam car so I can't give you a definitive answer on camber gain, I would say my top link was fairly parallel to the wishbone from memory.
Camber adjustment is purely to ensure even tire wear, so it is very common to have a different value on each wheel.

Marcos.J

iTrader: (235)

i may be silly for asking but is there any national/regional or world sanction races that use foams on tc classes? if not why waste time setting up cars if you will have to run rubber tires at those events,